DENVER , Colorado -LRB- CNN -RRB- -- A former hospital employee may have exposed hundreds , or even thousands , of surgical patients to hepatitis C after taking their fentanyl injections and replacing them with used syringes filled with saline solution , authorities say .

A hospital worker has admitted to secretly injecting herself and using unclean syringes for patients .

Kristen Diane Parker , who worked at Rose Medical Center in Denver , has admitted to secretly injecting herself in a bathroom and using unclean syringes as replacements for patients , investigators said .

She had hepatitis C , which she believes she contracted through using heroin and sharing dirty needles while she lived in New Jersey in 2008 , authorities said .

She was a surgical technician at Rose from October 2008 to April 2009 .

Nine patients who had surgery there during that time have tested positive for hepatitis C. Investigators are looking into whether they contracted the virus from Parker .

According to an affidavit filed by an investigator with the Food and Drug Administration , Rose Medical Center knew Parker tested positive for hepatitis C . She was counseled on how to limit her exposure to patients .

Parker quit after she was found to be in an operating room where she was not allowed to be . She subsequently tested positive for fentanyl . Hospital officials then contacted the DEA .

Parker is in federal custody facing three drug-related charges . If she is found to have done serious harm to a patient , she could face up to 20 years in prison . If a patient dies because of her actions , she could face life in prison .

In a statement to police , Parker said , `` I ca n't take back what I did , but I will have to live with it for the rest of my life , and so does everyone else . ''

Her attorney could not be reached Friday .

Rose Medical Center is contacting 4,700 patients who had surgery at Rose during the time Parker was employed there . However , hospital officials do not believe that many patients were exposed .

`` We are taking a very conservative and cautious approach by contacting everyone who had surgery during this broad time period , '' a statement on the hospital 's Web site said , adding , `` It is likely that most of the patients who receive letters will not have been exposed to hepatitis C. ''

An additional 1,200 patients may have been infected between May 4 , 2009 , and July 1 , 2009 , when Parker worked at Audubon Ambulatory Surgical Center in Colorado Springs . Audubon is also contacting patients .

According to the Centers for Disease Control , hepatitis C is a contagious liver disease that can lead to cirrhosis or liver cancer .

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Kristen Diane Parker believes she contracted hepatitis C from sharing dirty needles

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She was a surgical technician in Denver from October 2008 to April 2009

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Hepatitis C is a contagious liver disease that can lead to cirrhosis or liver cancer